Electric control system



Aug. 12, 1941. J. L. STRATTON ELECTRIC CONTROL SYSTEM Original Fil ed June 24, 1939 Inventor": Jerry L. Str tton,

s Attorney IL Q av Q a. Em. E V a. .a a, a Q a Patented Aug. 12, 1941 ELECTRIC CONTROL SYSTEM Jerry L. Stratton, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Original application June 24, 1939, Serial No. 280,924. Divided and this application July 23, 1940, SerialNo. 346,902

13 Claims.

My invention relates to electric control systems, such as regulating systems, and more particularly relates to regulators for electric valve apparatus.

This application is a division of my copending patent application, Serial No. 280,924, filed June 24, 1939, and assigned tothe assignee of this application.

I have found that it is frequently important in the control of dynamo-electric machines to regulate one operating condition of the machines, such as the speed, to maintain the speed within a predetermined range of values so long as the current supplied to the machine does not exceed a predetermined maximum value or decrease below a predetermined minimum value. When such maximum and minimum values are obtained, it is of importance to maintain the current at the limit values and to permit the speed to vary. In accordance with the teachings of my invention described hereinafter, I provide a new and improved electric control system for dynamo-electric machines whereby the speed of the machines is maintained substantially constant so long as the current transmitted to the machine remains within a predetermined range of values. In accordance with other aspects of my invention described hereinafter, I provide new and improved control apparatus for armature reaction excited dynamo-electric machines.

It is an object of my invention to provide a new and improved electric control system.

It is another object of my invention to provide a new and improved electric valve circuit for controlling a dynamo-electric machine of 'the armature reaction excited type.

It is a further object of my invention to pro- I vide a new and improved control system for dynamo-electric machines of the armature reaction excited type in which electric valve means is selectively controlled in response to two or more controlling influences.

Briefly described, in the illustrated embodiment of my invention I provide anelectric valve control system for dynamo-electric machines of the armature reaction excited type in which the dynamo-electric machine may be controlled in response to one or more separate controlling influences.

For a better understanding of my invention, r

reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. The single figure of the drawing diagrammatically illustrates an emtric machine.

bodiment of my invention as applied to a direct current motor for regulating the speed thereof and for controlling or limiting the maximum and minimum current values transmitted to the armature winding thereof.

Referring now to the single figure of the draw ing, my invention is there represented as applied to a system for regulating an operating condition, such as the speed, of a dynamo-elec- The machine to be controlled may be a direct current motor I having an armature winding 2, a series field Winding 3 and a shunt field winding 4. The shunt field winding 4 may be energized, if desired, from a separate source of direct current 5. The operating condition, such as the speed, of the motor i is controlled by suitable translating apparatus capable of transmitting a'variable voltage to'the armature 2 of motor I. This translating apparatus may comprise a direct current generator 6 driven by suitable means (not shown) having an armature winding I, a series field winding 8 and a second field winding, such as a shunt field winding 9. The motor I and the generator 6 are arranged in the conventional Ward-Leonard manner so that the speed of the motor l is controlled by variations in the energization of the field winding 9.

I provide an auxiliary dynamo-electric machine 10 which is of the armature excited type for variably energizing the field winding 9 of generator 6. The armature excited machine l0 may be termed an exciter which amplifies the variations in current transmitted to its control field winding H. The machine [0 may be provided with an armature winding 12 and is provided with two sets of brushes; one set of brushes, including brushes l3 and M, are short-circuited or connected through a conductor of low resistance and provide a path for the short circuit current which produces one component of the exciting flux of the machine. The other set of brushes, including brushes [5 andifi, produce a voltage which varies as the energization of the control field winding II. The voltage appearing across the brushes l5 and I6 is an amplified voltage relative to the voltage or current of the control field winding 'll. Field winding 9 of generator 6 is energized from the armature or the output of the machine ill.

The auxiliary dynamo-electric machine l0 may also be provided with additional windings. For example the machine may have a shunt winding Ha which establishes a magnetomotive force to assist that provided by the cross magnetomotive force produced by the armature current flowing through the connection between brushes I3 and I4. In addition, the machine It] may have a compensating winding IIc, the magnetomotive force of which opposes and substantially neutralizes the normal armature reaction. Machine IEI may also be provided with a commutating winding Ild. In order to assure the proper build-up of the voltage of machine I0, auxiliary bias or exciting winding IIb may be connected to produce a magnetomotive force which assists that provided by the compensating winding Ho and the control field winding II. curtain features of the dynamo-electric machine It! are disclosed and claimed in a copending application SerialNo. 281,008 of E. F. W. Alexanderson and M. A. Edwards, filed June 24, 1939, and which is assigned to the assignee of the present application.

As an agency for producing a voltage, such as a unidirectional voltage, which varies in accordance with the speed of the motor I, I provide a suitable arrangement, such as a tachometer or pilot generator I7, comprising an armature winding [8 and a field winding I9. The output of the pilot generator Il may be connected across a voltage divider 20, and a resistance 2| may be connected in series relation with the voltage divider. In order to provide a source of reference voltage against which the output voltage of the pilot generator I? acts, I employ a suitable arrangement, such as a rectifier circuit 22, which may comprise a transformer 23 energized from a suitable source of alternating current 24 and may include a voltage-doubling type of rectifier comprising a double-anode electric valve 25, capacitances 26 and 2i and a suitable constant potential device such as a glow discharge device 28. The voltage appearing across the terminals of the glow discharge device 28 remains substantially constant and serves as a reference potential against which the output voltage of the pilot generator I! acts. A resistance 29 and a capacitance 39 may be connected across the output terminals of the rectifier circuit 22, and an impedance, such as a resistance 3|, may be connected between one terminal of the capacitance 30 and the glow discharge valve 28. The potential difference between the conductors 32 and 33 remains substantially constant, and a predetermined component of the constant reference voltage furnished by the glow discharge device 28' is obtained through a voltage divider 34 which is connected to conductors 32 and 33 through a resistance 35, By the adjustment of the voltage dividers 20 and 34, the net voltage or the difference voltage between the output voltage of the tachometer pilot generator I! and the glow discharge device 28 may be adjusted.

To energize variably the control field winding II of the armature excited machine ID in response to the speed variations of the motor I, and to control the energization of control field winding II to maintain the speed of motor I substantially constant, I provide an electronic regulator 36. The electronic regulator 36 also limits the maximum and minimum current values transmitted to the armature winding 2 of the direct current motor I. That is, the electronic regulator 36 maintains the speed of the direct current motor I within a predetermined range of values or at a substantially constant value so long as the armature current transmitted to the armature 2 does not exceed or become less than the respective predetermined values. If the armature current tends to exceed this range of values, the speed is permitted to vary and the maximum or minimum value of armature current is maintained.

The electric valve system excluding the electronic regulator 36 is disclosed and claimed in my copending patent application Serial No. 351,- 970 which is a division of my application Serial No. 280,924.

Referring more particularly to the electronic regulator 36, I provide an electric valve means 31 which variably energizes the control field winding II by transmitting variable amounts of unidirectional current thereto from a suitable source of current, such as a direct current circuit 38. The electric valve means 31 -may be of the high vacuum type comprising an anode 39, a cathode 40, a control grid 4I and a screen grid 42, The screen grid 42 may be connected to a source of voltage positive with respect to the cathode 40. The voltage applied between the screen grid 42 and the cathode 40 and, of course, the voltage applied between the anode and the cathode may be controlled or adjusted by means of a suitable voltage divider 43 connected across the source 38.

The conductivity of the electric valve means 31 and hence the current transmitted to the control field winding I I are determined primarily by the potential impressed on the control grid M. This control potential is obtained by means of an impedance element, such as a resistance 44. Variable amounts of unidirectional current are transmitted through the resistance 44 to control the potential impressed on the control grid H. To provide a control system in which the conductivity of the electric valve means 3"! is controlled selectively in response to two different predetermined controlling influences, I provide a pair of electric circuits energized from the direct current circuit 38. One of these electric circuits includes a serially connected impedance element, such as a resistance 45, and an electronic discharge device 46; and the other circuit includes a serially connected impedance element, such as a resistance 41, and an electronic discharge device 48. Suitable points 01' connections of the two circuits are employed as points of reference potential. For example, I may employ common junctures 49 and 50 of the resistances 45, 4'! and electronic discharge devices 46, 48, respectively, as reference points. Electronic discharge devices 46 and 48 are preferably of the high vacuum type, each comprising an anode 5I, a cathode 52, a control grid 53, a screen grid 54, and a suppressor grid 55 which may be connected to th associated cathode 52.

I employ an electric valve means 56 for selectivel controlling the conductivity of the electric valve means 31 from that circuit of said pair of circuits which produces the predominating voltage in response to the respective related controlling influence. That is, the electric valve means 56 is provided with a pair of electric discharge paths associated with anodes 51 and 58 and the electrically common cathodes 59 thereof to energize the resistance 44 from that circuit of the pair of circuits which produces the predominating control potential. The feature oi using a double-anode or a double-cathode electric valve as a means for effecting selective control from the circuit providing the predomi; ating control voltage is disclosed and claimed in the U. S. Patent No. 2,019,352 granted October 29, 1935, upon an application of 0. W. Livingston, and which is assigned to the assignee of the present application. A capacitance 60 is connected across the resistance 44 to serve as a means for absorbing extraneous voltage variations. Screen grid 54 of electronic discharge device 46 is connected to the lower terminal of resistance 44 through a resistance 6|, and is also connected to the anode 39 of electric valve 31 through a resistance 62. These connections afford a feed-back arrangement between the electric valve means 31 and the electronic discharge devices 46 and 48. That is, there is a feed-back arrangement between electric valve 31 and discharge device 46 through resistance 62 and the screen grid 34, and there is also a feed-back arrangement between the electric valve 31 and the electronic discharge device 48. These feed-back circuits increase the sensitivity of the electronic regulator 36. vices, such as voltage dividers 63 and 64, may be associated with the electronic discharge devices 46 and 48, respectively, to adjust the potentials of the respective cathodes and to control the currents conducted through the associated circuits. The voltage divider 63 sets or establishes the maximum current limit of the regulator 36, and the voltage divider 64 establishes the minimum current limit for the regulater 36.

The electronic regulator 36 variably energizes the control field winding II of the machine III to maintain the speed of the motor I at a substantially constant value. This operation is effected by controlling the potential of the control grid 53 of the electronic discharge device 46. The variation in the potential of the control grid 53 may be'obtained by means of a suitable impedance element, such as a resistance 65, which is variably energized in accordance with the difference between the component of the output voltage .of the pilot generator I1 and a component of voltage derived from the constant voltage device 28. The unidirectional current transmitted through the resistance 65 varies in accordance with the speed of the motor I and controls the potential impressed on the control grid 53. A suitable current limiting resistance 66 may be connected in series relation with the control grid 53.

In order that the electronic regulator 36 maintain the speed of the motor I substantially constant within a predetermined range of values and in order that the regulator be controlled to limit the maximum and minimum energizations Suitable potential adjusting deof the armature winding 2 of motor I, I provide a suitable selective means, such as an electric valve means 61, which comprises a pair of elec tric discharge paths associated with anodes 66 and 69 and electrically common cathodes 10. Of course, it is to be understood that the discharge current will be carried by the discharge path on which there is impressed the predominating voltage. Anode 68 is connected to one terminal of the pilot generator I1, and anode 69 is connected to be responsive to the energization of the machine I. It will be noted that the anode 69 is connected to the common juncture H of the series field winding 3 and the armature winding 2 of motor I. Furthermore, the anode 69 is connected to the control grid 53 of the electronic discharge device 48. The electric valve 61 serves to control the relative amounts of current conducted by electronic discharge devices 46 and 46, that is, serves to control the relative conductivities of these discharge devices selectively in response to that controlling influence which produces the predominating control potential.

I provide an anti-hunting means connected between the output or armatur circuit of the armature excited machine Ill and the electronic regulator 36. This anti-hunting means may comprise a transformer 12 having a secondary winding 13, one terminal of which is connected to conductor 32 and the other terminal of which is connected to the cathode 52 of the electronic discharge device 46 through voltage divider 63. The transformer 12 is connected to modify the regulating action of the electronic discharge device 46 to prevent over-shooting or under-shooting of the speed of the motor I.

The operation of the embodiment of my invention shown in the single figure of the accompanying drawing will be explained by considering the system when it is operating to control the speed or the direct current -motor I. Of course, it will be understood by those skilled in the art that the speed of the motor I varies directly as the voltage applied to the armature winding 2, assuming that the energization of the field winding 4 remains substantially constant. The variable energization of the control field winding II controls the excitation of the generator 6 and hence controls the terminal voltage of that generator.

During normal operation, in which the energization of the armature winding I does not exceed the maximum or minimum limit, the control field winding II is variably energized to maintain the speed of the motor I substantially constant. The electric valve means 31 transmits variable amounts of current from the source 38 to the control field winding Ii,'and the conductivity of the electric valve means 31 is determined by the potential appearing acrossthe terminals of resistance 44. So long as the aforesaid current limits are not exceeded, the variations in speed of the motor I produce corresponding variations in the output voltage of the pilot generator I1 to cause variations in the amount of unidirectional current transmitted through resistance 65. Of course, during normal operation the discharge current is conducted between anode 66 and the cathode 10 and the variable control potential is impressed across control grid 53 and cathode 52.

As the speed varies, the conductivity of the electronic discharge device 46 also varies and the potential of connection 49 is raised or lowered to control the amount of current transmitted through resistance 44 which, in turn, controls the conductivity of the electric valve means 31. For example, if the speed of the motor I tends to increase above the desired value, the generated voltage produced by the pilot generator I1 also increases, thereby causing an increase of current transmitted through resistance 65. An in crease in current transmitted through the resistance 65 raises the potential impressed 0n control grid 63 of electronic discharge device 46' and, since the current through the resistance 45 is increased, the potential of the juncture 49 will be lowered. Consequently, the current transmitted through resistance 44 will be decreased and the conductivity of the electric valve means 31 will be correspondingly decreased. In this manner, the amount or current transmitted to the control field winding II is decreased, effecting a reduction in the current transmitted to field winding 6 of generator 6. As a result, the voltage applied to the armature winding 2 of motor I is decreased and the speed will be restored to the desired value. Conversely, as the speed of the motor I tends to decrease, it will be understood that the energization of the control field winding I I will be increased by the electronic regulator 36 to raise the speed of the motor I to the desired value.

During the above described normal range of operation, the current transmitted to the resistance 44 is, of course, conducted through a path including anode 58 of the electric valve means 56. The electronic discharge device 48 is maintained conductive during the normal range of operation to such an extent that the potential of the common juncture 50 and that of the anode 51 of electric valve means 56 are lower or negative relative to the potential of anode 58.

The electronic regulator 36 also operates to limit the maximum energization of the armature winding of motor I in the following manner: If the current transmitted to the armature winding 2 of motor I tends to exceed a predetermined value, the potential of the common juncture II of the armature 2 and field winding 3 rises, causing the control to be transferred from anode 68 to anode 69 or the electric valve means 61, in which case the control of the pilot generator I! is rendered ineffective. The potential of the control grid 53 of electronic discharge device 46 is limited so that the maximum current transmitted to the control field winding II remains substantially constant, thereby limiting the energization of the armature winding 2 of motor I. The operation of the regulator 36 which limits the maximum energization of the armature winding of motor 2 may be explained in the following manner. When the energization reaches a predetermined maximum value, causing anode 69 of the electric valve 61 to conduct, a circulating control current flows through a circuit including anode 69, cathode I0, resistance 65, armature winding I of generator 6 and armature winding 2 of motor I. It will be noted that the left-hand terminal of voltage divider 63 is connected to the negative terminal of circuit 38. If the current tends to increase above this maximum value, the circulating current temporarily increases and conductivity of the electronic discharge device 46 will be temporarily increased, effecting a reduction in the potential of anode 58 of electric valve 56 and effecting a corresponding decrease in the conductivity of the electric valve means 31. Consequently, the current transmitted to motor I will be decreased to the desired value. The potential applied to grid 53 of discharge device 46 under these conditions is the difiercnce between the voltage drop across field windings 3 and8 and the potential difference between the cathode 52 and the negative terminal of circuit 38. Therefore, the maximum potential variation of the grid 53 with re spect to the cathode 52 is limited to set a maximum limit to the current supplied to armature winding 2. The setting of the voltage divider 63 establishes the value of the maximum limit.

The electronic regulator 36 also operates to limit the minimum energization of the armature winding 2, thereby preventing a regenerative action between the motor I and the generator 6. If the armature current transmitted to motor I decreases below a predetermined value, it will be noted that the potential of the control grid of the discharge device.

53 of the electronic discharge device 46 is lovb ered, effecting a substantial decrease in conductivity of the electronic discharge device 48. As a result, the potential of the structure 50 will rise, causing the potential of anode 51 of the electric valve 56 to become more positive than that of the anode 58 and effecting a transfer in control to electronic discharge device 48 from the electronic discharge device 46. In this man ner, a minimum conductivity in the electric valve means 31 is assured and consequently a predetermined minimum current is assured for the energization of the control field winding I I. The energization of the armature winding of the motor I, therefore, is maintained at or above a predetermined minimum value. The value of the minimum current transmitted to the armature winding 2 is established by the setting of the voltage divider 64 since it determines the potential of the cathode 52 of discharge device 48.

The anti-hunting means, including the transformer I2, serves to prevent over-shooting of the regulatory action of the electronic regulator 36. The operation and the efiect of the anti-hunting means may be explained in the following manner. If it be assumed that the electronic regulator dictates an increase in the energization of the control field winding I I, the transformer I2 is connected to impress a transient positive voltage on the cathode 52 of the electronic discharge device 46, thereby tending to decrease the con ductivity of this discharge device and effecting a stabilizing action which tends to prevent overenergization of the control field winding II. Of course, if the electronic regulator 36 dictates a decrease in energization of the control field winding II, the transformer 12 impresses a transient negative voltage on the cathode 52 of electronic discharge device 46, thereby tending to prevent an under-shooting of the energization of the control field winding II. That is, the anti-hunting means acts as a stabilizing means to efiect a more precise control of the speed of the motor I under transient load conditions.

The feed-back connection between the anodecathode circuit of the electric valve means 31 and the screen grid 54 of the electronic discharge device 46 enables the regulator '36 to maintain accurately the speed of the motor 2, inasmuch as the circuit increases the sensitivity of the regulatory action. This eiiect, which is a positive feed-back, may be appreciated by considering the regulator 36 under these conditions when the electronic discharge device 46 is controlled by an increase of potential on the control grids 53, tending to increase the conductivity Upon such increase in the current conducted by the discharge device 46, the voltage impressed on the control member H of electric valve 31 will be decreased effecting a temporary rise in potential of the anode 39. ffhis rise in potential of the anode raises the potential of screen grid 54 and accordingly increases the sensitivity of the regulator,

The armature excited machine III operates as an electromagnetic amplifier; that is, small variations in the current transmitted to the control field winding II produce a highly amplified variation in the output of'machine ID. The control field winding II produces a magnetomotive force having a component displaced electrical degrees relative to the cross magnetomotive force produced by the short-circuit current which flows in the armature winding I2 due to the connection between brushes I3 and H. The object of the control field winding H is to permit the output voltage appearing across brushes l and I6 to be varied without introducing additional controlling means in the armature circuit. The control field ll efiects con trol of the current output of the armature winding [2; and, as stated above, there is obtained a substantial amplifying effect between the energization of the control field winding H and the output circuit of the machine Ill. The value of the output current of machine I0, for a given input voltage impressed across the control field winding H may be varied by varying the control field current, or course, it is to be understood that the armature excited machine I0 is driven mechanically. In the embodiment of the invention shown, the armature of the machine [0 may be connected mechanically to the gen erator 6 or to the means which drives the gen- I erator 6. The machine l0 responds very rapidly to changes in field energization to produce changes in output current. Of course, the input current or changes in input current will be amplified.

While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention,

1 and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source of current, a load circuit, a dynarno-electric machine of the armature reaction excited type having an armature winding connected to said load circuit and having a control winding, electric valve means connected between said source and said control winding for controlling the current transmitted to said load circuit, said electric valve means having a control member, an impedance element, an electronic discharge device of the controlled type for transmitting variable amounts of current from said source through said impedance element to control" the voltage impressed on said control member, means for controlling. the conductivity of said electronic discharge device, a

second electronic discharge device for transmitting variable amounts of unidirectional current from said source through said impedance element, a pair of unidirectional conducting paths connected between said first mentioned and said second mentioned electronic discharge devices and said impedance element for selectively deriving control from that discharge device providing the predominating control voltage, and means for controlling the electric discharge devices comprising' a second pair of unidirectional conducting paths selectively responsive to two diiierent predetermined controlling influences.

2. In combination, a source of current, a load circuit, a dynamo-electric machine of the armature reaction excited type having an armature winding connected to said load circuit and having a control winding, electric valve means connected between said sourceand said control winding for controlling the current transmitted to said load circuit, said electric valve means having a control member, means for producing a plurality of relativel variable control potentials which are responsive respectively to difierent predetermined controlling influences, an impedance element, an electric valve means having a pair of electric discharge paths connected in circuit with said impedance element, an electronic discharge device of the controlled type for controlling the voltage impressed across one of the discharge paths of said electric valve means to transmit variable amounts of current through said impedance element and to impress a variable control potential on said control member, a second electronic discharge device of the controlled type for impressing across the other of. said discharge paths a control potential, and means for controlling the electronic discharge devices comprising electric valve means having a pair of discharge paths selectively responsive to that controlling influence providing the predominating control potential.

3. In combination, a source of direct current, a load circuit, a dynamo-electric machine of the armature reaction excited type having an armature winding connected to said load circuit and having a control winding, an electric valve means having a control member for transmitting variable amounts of current to said control winding from said source, a pair of electric circuits for producing control potentials and connected to be energized from said source and each comprising a serially connected resistance and an electronic discharge device of the controlled type comprising at least one control grid, means for energizing the control grids, and means connected between said circuits and said control member for effecting selective control of said electric valve means from that circuit producing the predominating control potential comprising an impedance element and an electric valve means having a pair of electric discharge paths each of which is associated with a different one of said electric circuits.

4. In combination, a source of direct current, a load circuit, a dynamo-electric machine of the armature reaction excited type having an armature winding connected to said load circuit and having a control winding, an electric valve means having a control member for transmitting variable amounts of current to said control winding from said source, a pair of electric circuits for producing control potentials and connected to be energized from said source and each comprising a serially connected resistance and an electronic discharge device of the controlled type comprising at least one control grid, means connected between said circuits and said control member for effecting selective control of said electric valve means from that circuit producing the predominating control potential comprising an impedance element and an electric valve means having a pair of electric discharge paths each of which is associated with a different one of said electric circuits, means for producing two relatively variable control potentials which are responsive respectively to two different controlling influences, and means for effecting selective control of the relative conductivities of said first mentioned and said second mentioned electronic discharge devices through the associated control grid in response to the predominating control potential of said last mentioned control potentials and comprising an electric valve means having a pair of electric discharge paths each of which is responsive to a different one of said last mentioned control potentials.

5. In combination, a source of current, -a load circuit, a dynamo-electric machine of the armature reaction excited type having an armature winding connected to said load circuit and having a control winding, an electric valve means having an anode, a cathode and a control member for transmitting variable amounts of current to said control winding from said source, a pair of electric circuits for producing control potentials and connected to be energized from said source and each comprising a serially connected resistance and an electronic discharge device of the controlled type comprising a pair of control grids, means for energizing one control grid of each of the discharge devices. means connected between said pair of circuits and said control member for eiiecting selective control of said electric valve means from that circuit producing the predominating control potential comprising an impedance element and an electric valve means having a pair of electric discharge paths each of which is associated with a diiferent one of said electric circuits, and a feed-back circuit connected between the anodecatliode circuit of said first mentioned electric valve means and the other control grid of at least one of the electronic discharge devices,

6. In combination, a source of current, a load circuit, a dynamo-electric machine of the armature reaction excited type having an armature winding connected to said load circuit and having a control winding, electric valve means connected between said source and said control winding for controlling the energization of said load circuit and comprising an anode, a cathode and a control member, means for impressing on said control member a control voltage comprising an electronic discharge device having two control grids, means for impressing on one of said control grids a voltage variable in response to a predeterminedcontrolling influence, and a feedback means connected between the anodecathode circuit of said electric valve means and the other control grid.

7. In combination, an electric circuit, a dynamo-electric machine of the armature-excited type having an armature winding provided with at least two sets of brushes, one set of said brushes being connected to said circuit and the other set being substantially short-circuited, said machine having a control field winding for estab lishing a magnetomotive force having a component at ninety electrical degrees relative to the axis of the magnetomotive force which is furnished by the current which flows in said armature winding due to the connection between said other set of brushes, and electric valve means for variably energizing said control field winding.

8. In combination, an electric circuit, a dynamo-electric machine of the armature-excited type having an armature winding provided with at least two sets of brushes, one set of brushes being connected to said circuit and the other set being substantially short-circuited, said machine having a control field winding for establishing a magnetomotive force having a component at ninety electrical degrees relative to the axis of the magnetomotive force which is furnished by the short-circuit current which flows in said armature winding, electric valve means for controlling the energization of said control field winding, and means for controlling the conductivity of said electric valve means to control the energization of said electric circuit.

9. In combination, an electric circuit, a dynamo-electric machine of the armature reaction excited type having an armature winding provided with at least two sets of brushes, one set of said brushes being connected to said circuit and the other set being substantially short-circuited, said machine having a control field winding for establishing a magnetomotive force having a component at ninety electrical degrees relative to the axis of the magnetomotive force which is furnished by the current which flows in said armature winding due to the connection between said other set of brushes and having a compensating winding connected in circuit with said electric circuit and said one set of brushes to produce a magnetomotive force which substantially neutralizes the secondary armature reaction, and electric valve means responsive to an electrical condition of said circuit for variably energizing said control field winding,

10. In combination, an electric circuit, a dynamo-electric machine of the armature reaction excited type having an armature winding provided with at least two sets of brushes, one set of brushes being connected to said circuit and the other set being substantially short-circuited, said machine having a control field winding for establishin a magnetomotive force having a compo nent at ninety electrical degrees relative to the axis of the magnetomotive force which is furnished by the short-circuit current which flows in said armature winding and having a cornpensating winding connected in circuit with said electric circuit and said one set of brushes to produce a magnetomotive force which substantially neutralizes the secondary armature reaction, electric valve means for controlling the energization of said control field winding, and means responsive to a predetermined controlling infiuence for controlling the conductivity of said electric valve means to control the energization of said electric circuit.

11. In combination, a load circuit, an armature reaction excited machine for energizing said load circuit and comprising an armature winding provided with at least two sets of brushes and having a control winding, one set of said brushes being connected to said load circuit and the other set being substantially short-circuited, electric translating apparatus comprising electric valve means for controlling the energization of said control winding, said electric valve means having a control grid, control means for impressing on said control grid a voltage which varies in response to a predetermined controlling infiuence, and means for controlling said electric valve means to render said control means ineffective so that constant current is transmitted to said control winding.

12. In combination, a load circuit, an armature reaction excited machine for energizing said load circuit and comprising a control winding and an armature winding provided with at least two sets of brushes, one set of brushes being connected to said load circuit and the other set being substantially short-circuited, electric translating apparatus comprising electric valve means having a control grid, control means for impressing on said control grid a voltage which varies in response to a predetermined controlling influence, and anti-huntin means responsive to an electrical condition derived from said machine for controlling the rate of change of said voltage.

13. In combination, a load circuit, an armature reaction excited machine having an armature winding provided with at least two sets of brushes and having a control winding, one set of brushes being connected to said circuit and the sponse to a predetermined controlling influence,

and anti-hunting means responsive to the rate of change of the armature current of said ma.- chine for modifying the regulatory action of said 5 voltage.

JERRY L. STRATTON. 

